The present invention relates to a process for the production of a photopolymerizable recording material, in particular a dry photoresist material comprised of a layer support and a solid, dry photopolymerizable layer which contains, as the essential constituents,
(a) a polymeric binder which is insoluble in water and soluble in aqueous-alkaline solutions,
(b) an acrylic or methacrylic acid ester of a polyhydric alcohol, which is polymerizable by a free-radical process, and
(c) an initiator capable of photo-inducing the free-radical polymerization.
The free surface of the photopolymerizable layer is preferably covered with a thin polyethylene film.
Materials of the above-mentioned type are disclosed, for example, in U.S. Pat. No. 3,469,982, and are extensively used in the production of printed circuits and in similar applications.
The photoresist layers of these materials must be adapted for dry transferring to another support material, for example, a copper plate, with the application of pressure and usually also with heating. Therefore, the photoresist layer must be at least thermoplastically deformable, preferably even plastically deformable at ambient temperature, and it should have a particular tackiness. Materials showing these processing characteristics to an optimum degree present certain problems during storage and transport in the unexposed state, since their photoresist layers invariably tend to undergo some cold flow which becomes apparent when the material is stored in the form of a roll. The photoresist layer then emerges between the film layers at the end faces of the roll and causes the wound-up layers. to stick together. In an attempt to solve this problem, the composition of the photoresist layer, in particular the nature of the thermoplastic binder, has been modified to raise the flow temperature of the layer. This way of proceeding, which is described, for example, in German Offenlegungsschrift No. 23 63 806, is limited by the fact that the brittleness of the photo-crosslinked layer increases with a rising flow temperature of the unexposed layer, such that processing of the exposed material is rendered difficult.
Another solution to the problem is described in German Patent No. 23 45 120. According to this publication, the edges of the photoresist layer are light-hardened, so that the layer can no longer be squeezed out. This method has the disadvantage that, during processing of the respective material, light-sensitive substance is lost in the edge zones, since a particular safe distance must be allotted to ensure that any partly polymerized portions of the layer are excluded from the subsequent exposure and developing.
To overcome this problem, it is proposed in German Patent Application No. P 34 37 453.1 to cover the end faces of the dry resist rolls by means of glued-on covering disks, in order to prevent any photopolymerizable layer portions from being squeezed out during storage.